Indicating device for measuring instruments



Jully 18, H1933. F PFAU INDICATING DEVICE FOR MEASURING INSTRUMENTS Filed May l, 1931 ILVerzaP:

Patented July 18, 1933 UNITED STA TEs FRIEDRICH PFAU, OF- JENA., GERMANY, ASSIGNOB T0 THE FIRM 0F CARL ZEISS, OF l JENA, GERMANY INDICATIN G DEVIGE FOR MEASURING INSTRUMENTS Application med Hay 1, 1931, Serial No. 534,313, and in Germany May/8, 1930.

With measuring instruments furnished with scale and index it is the general practice to have the limits of 'tolerance indicated by two marks adjustable along the scale. Material marks covering as they 'do a certain part of the scale will frequently not permit of seeing with the required exactnessthe index positions at the limits. The present invention overcomes this vdrawback by using as limit marks the edges of at least one light filter which is displaceable .parallel to the plane of the scale-and offers the advantage of the visibility of the Covered part of the scale being impaired only to a slight extent. When using a single light filter, and when the scale is given, the space between the limits is 1nvariable and independent of the position of this space relative to the scale. A filter consisting of two parts, however, makes it possible to alter not only the position of the limits relatively to the scale but also the space between the limits.

With optical measuring instruments which are used principally in transmitted light and together with an optical index and a yscale provided in one image plane of the instrument it is advisable to take as limit marks the edges of two strips of glass, Celluloid or other suitable material having a slightly absorbing effect for at least part of the visible spectral ran of the light rays and to make these strips displaceable from the ends of the scale and in close proximity to the planeof` this scale. For this purpose for instance -slightly coloured glasses or lasses of a reyish tone may be used. I instead o the material scale and the ,material limit marks the-optical image of one or two of thesel elements is used, the parallax canvbe avoided by arranging these elements in one plane and not in two planes close together.

The accompanying drawing re resents a constructional example of the ocu ai' end of an `o tical measuring instrument, which is furnlshed with the indicating device according to the invention. Figure 1 illustrates the instrument in front elevation, partly in a central section, and Figure 2 re resents a cross'section along line 2 2 in igure 1.

The optical measurin instrument a is equipped with an adjusta le ocular b havin ing) and the shadow image e of a line in the plane of tlie scale serves as an index. The tube of the ocular isenclosed in a ring f fast with two tubular fittings g1, g2. These fittings g1, g2 are'hollow and their axis falls in the direction of the scale (Z. In the fittings g1,

' g2 threaded bolts h1 and, respectively, k2 are displaceable by means of internally threaded heads 1 and, respectively, i2.' In the ends of the bolts h1, h1 areprovided slits k1 and,

respectively, k2 in which screws m1 and, re-

spectively, m2v are 'made to hold slightly, coloured thin glass strips Z1 and, respectively, Z2. The glass strips Z1, Z2 extend through slits n1 and, respectively, 'n1' into the'ocular tube and are closeto the plane of the scale d on the glass plate c. 'The heads of the screws m1, m2 go through slits 01 and, respectively, o2

. provided in the fittings g1v and, respectively,

g1 and prevent the screws. 71,1, 7L from being turned.

An observer looking through the ocular b of the measuring instrument a is confronted with the view-of the image illustrated by F i re 2. By means of knobs i1, 2 the glass str1ps Z1, Z1 ar adjusted with respect to their positions .rel tive to the scale d so as to suit the desired limits of tolerance. The limits of' tolerance for the play ofthe index e are indicated by the'edges of the glass strips Z1, Z2, which are parallel to the devision lines of the scale d. The glass strips Z1, Z2 permit of seeing also that part of the scale cZ which lies outuol side the limits-of tolerance as well as the ments, the light filter comprising two parts and means for adjusting each ofthe parts'j of the filter from either end of the scale.

` FRIEDRICH PFAU.

1n its ocular image planea glass plate c wit a sca'le d. The lass plate c is in the wellk'nown manner illuminated from below intransmitted light (not shown in the draw- 

